Innovative Underground Works at Madeira Island, Portugal

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1 Innovative Underground Works at Madeira Island, Portugal Paulo Cafofo 1, L. Ribeiro e Sousa 2, Francisco Moura 3 1 Electricity of Madeira, Funchal, Portugal 2 University of Porto, Porto, Portugal 3 University of Minho, Guimarães, Portugal ABSTRACT The extremely mountainous and the heterogeneous volcanic rock formations of the Madeira Island led to the construction of an important road network where the tunnels are dominants. Unique and innovative solutions were also developed for multi-purpose hydraulic and hydroelectric systems. 1. INTRODUCTION The extremely mountainous and the heterogeneous volcanic rock formations of the Madeira Island led to the construction of an important road network where the tunnels are dominants. Unique and innovative solutions were also developed for multi-purpose hydraulic and hydroelectric systems. The road tunnels of new transport system of Madeira Island were strongly affected by the heterogeneous and complex volcanic formations, by the topography and by the land occupation. All these factors originate the design of a large variety of innovative structural solutions that permitted to achieve economic solutions more adequate to the topographic and geological local conditions. The new road transport network permitted an easy and comfortable access to the whole island. The regional road system length is about 546km, of which around 78km are in tunnel. However, in the new highways the ratio of tunnels is about 43%, in a total of 173km. More important works are still planned, mainly in the Northern part of the island. In this paper, the analysis of a road tunnel between Caniço and Camacha is presented, along with the description of the construction and of the geotechnical information. Finally a UPHS innovative Socorridos hydroelectric scheme that is a part of a multi-purpose scheme at Madeira Island is described. The upper and down reservoirs are totally underground as well as the pumping station. 2. ROAD TUNNELS IN MADEIRA ISLAND The road tunnels of new transport system of Madeira Island were strongly affected by the complex volcanic formations, the topography and the land occupation. All these factors originate the design of a large spectrum of innovative structural solutions that permit to achieve economic solutions more adequate to these restriction conditions. The new road transport network, with high radii curves and more reduced longitudinal inclinations permitted easy and comfortable accesses to the whole island. In the new highways the relation is about 43% in tunnels, in total of 173km. More important works are still planned, mainly in the Northern part of the island, also with an important of these being tunnels (Moura and Sousa 2006; Menezes et al., 2007). The geology of Madeira Island comprises five volcanic complexes (Figure 1): 137

2 β1 - mio-pliocenic volcanic complex of Curral das Freiras, Serra de Água, Vale de São Vicente and Vale da Boaventura, in west part of the island and Ruivo e Areeiro mountains, São Roque, Porto da Cruz, Machico and Ponta de São Lourenço. β2 - pos-miocenic volcanic complex at Ribeira da Janela, Porto Moniz, Ponta do Pargo, Ribeira Brava and Câmara de Lobos, in the west part, and Funchal, Camacha, Santa Cruz and Santana, including tuffs at Arco de São Jorge. β3 - pos-miocenic volcanic complex of Paúl da Serra, Achada da Pinta and Lombada das Vacas, at west part, and Lombada do Meio, Cabeços de Fajã dos Vinháticos and Terreiro da Luta, in the east part of the island. β4 - superior basaltic complex of Paúl da Serra, Chão dos Balcões, Poiso and Achada do Teixeira. β5 - modern basaltic lava of Porto Moniz and the valleys of São Vicente and Seixal. Fig. 1. Geological-geotechnical formations at Madeira Island. The transversal section of the road tunnels at Madeira Island Region has a horse-shoe (semi-circular arch) cross section with a span of 9.0m, for tunnels with one direction of traffic and 9.6m for tunnels with two directions of traffic. Both types of tunnels consist of two lanes with a width of 3.5m. In some older tunnels a semi-elliptic arch was adopted (João Gomes and Jardim Botânico tunnels). Some tunnels may have up to three (Pestana Júnior tunnel) or four lanes (Santa Cruz West and East tunnels). Here the width is 18.5m, in order to allow 2 lanes in each direction, separated by a central separator. Figures 2 and 3 presents examples of geometric characteristics for the one traffic directional road tunnels constructed at Madeira Island. Fig. 2. Tunnel with two lanes. Fig. 3. Tunnel with two lanes. 138

3 3. ROAD TUNNEL BETWEEN CANIÇO AND CAMACHA In order to establish a road liaison between Cancela and Nogueira located in the towns of Caniço and Camacha, respectively, important viaducts and tunnels were constructed in a mountainous region of Madeira in an extension of about 3.9km. Of these an extension of 2.44km (63% of the total) consisted of four tunnels. They have two directions of traffic with a lane in each direction (until km including Tunnel 1) and with two lanes in the North direction (since km 0+725) for heavy traffic. This paper is focus in Tunnel 2. Two sections are being considered, A (km 1+167) and B (km 1+256). Section A crosses a zone of disaggregated to moderate compacted breccias. Section B corresponds to a zone of disaggregated and compact breccias, and compact basalts. The support design adopted for the different types of rock formations was based on empirical methodologies (Menezes et al., 2007). In this tunnel supports used on both sections A and B were the following: bolts length of 4m, 20mm in diameter with a capacity of 177kN, 1.5m spacing in the roof and 2.0m in the walls for section A and 1.0m for section B; shotcrete 10cm in thickness on section A and 5cm on section B; steel linings only on section A, a profile HEB 160 spacing of 0.8 in upper part of the section. As usually done at Madeira Island a final concrete support was adopted with a thickness of 30cm. The construction process adopted was the Sequential Excavation Method (SEM). Due to the strong heterogeneity of the volcanic formations the construction was versatile in order to be adaptable to the different geotechnical conditions. Section A of Tunnel 2 has an overburden of about 3.9m, composed by rock material of weak geomechanical quality. The construction sequence is illustrated in Figure 4. Section B has an overburden of 26m composed of basalt of good geomechanical characteristics. The construction sequence is presented in Figure 5. Fig. 4. Construction sequence for section A. Fig. 5. Construction sequence for section B. Tunnel 2 is located in the volcanic complex β 2 that is composed of basalts and of piroclastic materials with variable dimensions like tuffs, breccias and scoria. The geotechnical survey of the tunnel consisted of boreholes and laboratory tests. The deformability and strength properties were estimated based on laboratory tests results. The results from the survey show highly complex heterogeneous formations for complex β 2 with different types of formations besides the surface soil formations, that were 3m thick: Compact basalt predominant lithology with a weathering degree between W3 to W1-2; RQD between ; E = [17-46] GPa and σ c =[35-100]MPa. Volcanic breccias also an important lithology with a matrix highly variable, more or less compact. The weathering degree varies between W4 to W3; RQD is in average 50, being null in the disaggregated breccias; E= [0.1-33]GPa and σ c =[1-35]MPa. Volcanic tuffs a less important lithology appearing in the upper part of the rock mass. The weathering degree varies between W4-5 to W3; RQD is in average 60, with a wide spectrum; E=[0.1-5]GPa and σ c =[0.9-18]MPa. 139

4 The geomechanical parameters were determined through the RMR empirical system. Relevant average geomechanical parameter values are presented in Table 1. Probabilistic approaches and the software developed for underground construction designated GEOPAT were used to obtain a probabilistic distribution and average values (Costa et al. 2002; Miranda et al. 2005). The structural analysis of Tunnel 2 was performed using software Phases2 from Rockscience for 2D analysis and FLAC 3D from Itasca, for the 3D analysis. The two referred sections A (portal section) and B (inside the rock mass) were considered (Menezes et al., 2007). The in situ state of stress adopted considered a ratio of 0.8 between in situ state horizontal and vertical. The maximum settlement observed at the tunnel crown was about 5.8mm and the maximum convergences measured were equal to 10,0mm. Settlements at the surface were also evaluated in order to assess any possible damage on the buildings. The yielded zones were evaluated. They are mainly located in the disaggregated breccia that exhibited low strength. Table 1. Geomechanical parameters. Section A Parameter Disaggregated breccia Moderate compact breccia γ (kn/m 3 ) E (GPa) σ c (MPa) m b (HB crit.) s (HB crit.) 5.44x Section B Parameter Disaggregated breccia Compact breccia Compact basalt γ (kn/m 3 ) E (GPa) σ c (MPa) m b (HB crit.) s (HB crit.) 5.44x Mention is made to an empiric system developed specifically for the volcanic rock formations. It was adapted from the RMR system and from a classification developed at IPT, São Paulo, for the design of several tunnels in basaltic formations (Ojima 1981). For more details on this system see Menezes et al. (2007). 4. UPHS SOCORRIDOS HYDROELECTRIC SCHEME Madeira Electricity Company decided to repower the Socorridos hydroelectric scheme that is integrated in a multiple purpose scheme with the same name. The hydroelectric complex is equipped with reversible units with a differential elevation of about 450m between the Covão upper tunnel and the lower storage tunnel. The rock mass involved is predominantly basaltic. The repowering included the following sequence of underground works: i) a 5.2km tunnel located at upper level (Covão tunnel); ii) a gallery for storage of water with a total capacity of m 3 ; iii) a cavern pumpage station, where are located the pumpage equipments. The Covão tunnel allows besides the purpose of water supply and irrigation an upper pressure gallery for the Socorridos hydroelectric powerhouse. It has an extension of 5244m and a storage capacity of about m 3 (Figure 6). Initially has a length of 100m excavated by drill and blasting method with a section of 4.20x3.60m 2, through the Campanário side. The remaining 5144m were excavated by a TBM with a diameter of 3.016m being the tunnel circular with a final diameter of 3m. The tunnel presents two inclinations, one with 0.038% until PM 4.729, and afterwards an inclination of 1.8%. 140

5 11th ACUUS Conference: Underground Space: Expanding the Frontiers, September , Athens - Greece N W E S Fig. 6. Plan and longitudinal cross section of Covão tunnel. Figure 7 presents a typical cross section of the Covão tunnel with radium of 3.0m, as well as a detail of the final support. The tunnel was designed in a complex topography region, in the volcanic complex β2 identified in the Geological map of the island (Menezes et al., 2007). The ground crossed by the tunnel consists of basalts, breccias and tuffs. The geomechanical classification of the volcanic formations is presented at Table 2. Fig. 7. Typical section of Covão tunnel. Table 2. Geological-geotechnical zones for the Covão tunnel. Zones Lithologies ZG1 ZG1A Compact basalts ZG1B Fractured basalts ZG2 ZG2A Consolidated breccias ZG2B Desagregated breccias ZG3 ZG3A Compact tuffs ZG2B Desagregated tuffs 141

6 Pumping station Fig. 8. Plan of lower tunnel reservoir. Fig. 9. Location of the pumping station. The hydroelectric scheme of Socorridos is reversible, thus the lower underground reservoir was excavated with the extension of 1200m (Figure 8). The pumping stations were located underground as indicated in Figure 9. Cross sections are illustrated at Figure 10. More details about the characteristics of these underground works are presented in Cafofo and Sousa (2007). Fig. 10. Cross sections of the pumping station 5. CONCLUSIONS A reference is made for the important highway network at Madeira Island recently built. The percentage of tunnel length is perhaps unique. A behavior analysis of a road tunnel recently constructed in Madeira Island was described. It is part of the connection Caniço-Camacha and it was constructed in volcanic formations. Finally, the innovative solution adopted for the UPHS Socorridos hydroelectric power scheme is emphasized. 142

7 ACKNOWLEDGEMENT The authors are greatly indebted to Electricity of Madeira and to the Road Regional Direction of the Autonomic Region of Madeira for authorizing the publication of this paper. REFERENCES Cafofo, P.; Sousa, L.R Innovative underground works at Socorridos, Madeira Island, Portugal. 2 nd Int. Workshop on Volcanic Rocks, Ponta Delgada (to be pubçlished). Costa, P.; Monteiro, A.; Oliveira, R.; Gaião, R.; Baião, C.; Sousa, L.R Geotechnical analysis of the Caniçal tunnel, Madeira Island. ISRM Symposium EUROCK 2002 on Rock Engineering for Mountainous Regions, Funchal, Ed. D. Gama and R. Sousa, pp Menezes, A.T.; Varela, F.M., Sousa, L.R., Moura, F. (2007). Geomechanical studies for a road tunnel in volcanic formations. ITA Congress, Prague (to be published). Miranda, T.; Correia, A.; Sousa, L.R.; Lima, C Numerical modeling of a large underground powerhouse using geomechanical parameters obtained by artificial intelligence techniques. ISRM Int. Symposium on Contribution of Rock Mechanics to the New Century, Kyoto, Ed. Y. Ohnishi & K. Aoki, pp Moura, F., Sousa, L.R The road tunnels in Madeira. Methodologies of construction and safety. University of Minho, Individual Project, Guimaraes, 14p. Ojima, L.M Methodology of rock mass classification applicable to tunnels (in Portuguese). LNEC thesis, Lisbon. 143